1. Field of the Invention
The present invention relates to an ink composition suitably used for inkjet recording, an inkjet recording method, and a printed material employing same; furthermore, it relates to a lithographic printing plate obtained using the ink composition, and a process for producing a lithographic printing plate. More particularly, it relates to an ink composition suitable for inkjet recording that cures with high sensitivity upon exposure to radiation, can form a high quality image, and has little unpleasant odor originating from an ink component (hereinafter, abbreviated to odor), that is, a so-called low odor ink composition, an inkjet recording method, a printed material employing same, a lithographic printing plate obtained using the ink composition, and a process for producing a lithographic printing plate.
2. Description of the Related Art
With regard to an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic system, sublimation type and melt type thermal transfer systems, an inkjet system, etc. In the electrophotographic system, a process of forming an electrostatic latent image on a photosensitive drum by electrically charging and exposing is required, and the system is complicated; as a result, there is the problem that the production cost is high. With regard to the thermal transfer system, although the equipment is inexpensive, due to the use of an ink ribbon there is the problem that the running cost is high and waste material is generated. On the other hand, with regard to the inkjet system, the equipment is inexpensive and, since an image is formed directly on a recording medium by discharging an ink only on a required image area, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording system.
An ink composition that can be cured by exposure to radiation such as ultraviolet rays and, in particular, an inkjet recording ink (radiation curing type inkjet recording ink) are required to have sufficiently high sensitivity and provide a high image quality. By achieving higher sensitivity, a large number of benefits are provided, such as high curability toward radiation, a reduction in power consumption, longer lifetime due to a decrease in the load on a radiation generator, and prevention of formation of low molecular weight material originating from insufficient curing. Furthermore, higher sensitivity particularly improves the cure strength of an image formed using the ink composition and, in particular, the inkjet recording ink, particularly for the formation of a lithographic printing plate, and high plate life can be obtained.
Such a UV-curing inkjet system, which can be applied to recording on a recording medium that does not have quick drying properties or ink absorbing properties, has recently been attracting attention, and UV-curing inkjet inks have been disclosed (ref. e.g. JP-B-5-54667, JP-A-6-200204, Published Japanese translation No. 2000-504778 of a PCT application; JP-A denotes a Japanese unexamined patent application publication, and JP-B denotes a Japanese examined patent application publication).
With regard to the UV-curing ink, there is a type comprising a radically polymerizable monomer, and a type comprising a cationically polymerizable monomer. For many of the type comprising a radically polymerizable monomer, the monomers used have an odor, and the odor is a problem. On the other hand, the cationically polymerizable monomers have a relatively low odor, but there are some that have an odor.